1. Field of the Invention
The present invention relates to a lighting device, and more particularly to a lighting device capable of changing light patterns.
2. Description of the Related Art
U.S. Pat. No. 6,986,593 discloses a lighting device using a reflector and a primary lens to shape a light pattern. However, as the light pattern of this prior art is controlled by using a motor to drive a cylinder to determine a focal length, its power consumption can't be small, and its structure is kind of awkward.
Recently, tunable lenses such as tunable liquid crystal microlenses or tunable optofluidic devices (TOD) using liquid lenses have been utilized in providing variable light patterns. However, heat dissipation can be an issue for lighting devices utilizing tunable lenses. The performance of the light source of a lighting device utilizing a tunable lens can be compromised if the heat of the light source is not dissipated efficiently. Take LEDs for example. The junction temperature of an LED can affect the lighting efficiency and lifetime of the LED. With the junction temperature increasing 10° C., the lifetime will reduce 25% and the lighting efficiency will drop 2.5%.
To tackle the heat dissipation issue, US patent Pub. No. 2010/0277923 locates a light source atop a liquid lens element. The liquid lens element includes a main body having a liquid chamber formed therein. A lens surface changes orientation of light that exits the light exiting surface by being electrically deformed, and the lens surface is formed of an interface between two liquids that are contained in the liquid chamber and have different refractive indexes. A first liquid of the two liquids is conductive, and an electorwetting force caused by a voltage can be acting on the first liquid to change the curvature of the lens surface.
However, as the light source and the liquid lens element of US patent Pub. No. 2010/0277923 are located in different compartments, the electrical wiring for the light source and the liquid lens element is not convenient, and the overall structure is not compact enough.
In view of the foregoing problems, a more compact and efficient lighting device is therefore needed.